1. Field of the Invention
This invention relates to a hybrid drive unit for vehicles having a plurality of prime movers such as an engine and a motor generator.
The disclosure of Japanese Patent Application No. 2004-150845 filed on May 20, 2004 including specification, drawings and claims is incorporated herein by reference in its entirety.
2. Discussion of the Related Art
A hybrid vehicle, which has an engine and a motor generator as a prime mover, is known in the art. This kind of hybrid vehicle is capable of improving the fuel consumption and abating emission by utilizing the characteristics of the engine and the motor generator. One example of the hybrid vehicle thus having the engine and the motor generator as a prime mover is disclosed in Japanese Patent Laid-Open No. 2000-346187.
The hybrid vehicle disclosed in Japanese Patent Laid-Open No. 2000-346187 comprises an engine and an assist motor as a prime mover, and a planetary gear mechanism is arranged between the engine and a drive shaft. The planetary gear mechanism comprises three rotary elements such as a sun gear, a ring gear, and a carrier holding a pinion gear meshing with the sun gear and the ring gear. In the planetary gear mechanism, the carrier is connected to the engine side, and the ring gear is connected to the drive shaft. The assist motor is also connected to the drive shaft, and a motor is connected to the sun gear.
There is provided a transmission in the route from the engine to the carrier. The transmission comprises three rotary elements such as a sun gear, a ring gear, and a carrier holding a pinion gear meshing with the sun gear and the ring gear. In the transmission, the carrier of the transmission is connected to the engine, and the ring gear of the transmission is connected to the carrier of the planetary gear mechanism. Moreover, there are provided a clutch for allowing integral rotation between the carrier and the ring gear of the transmission, and a brake for selectively halting the rotation of the sun gear of the transmission. Additionally, a battery is connected to the motor and the assist motor.
The torque outputted from the ring gear is transmitted to the drive shaft by using the motor to function as a reaction element while inputting an engine torque to the carrier of the planetary gear unit. The motor functioning as the reaction element carries out a regenerative control (i.e., an electric power generating control), and generated electric power is stored in a battery. It is possible to control a speed change ratio steplessly by controlling the speed of the motor. Here, the speed change ratio is a speed ratio of the carrier of the planetary gear unit and the ring gear of the planetary gear unit. Namely, the planetary gear unit functions as a continuously variable transmission utilizing a differential action of the three rotary elements. It is also possible to fill in the gap between a demand torque of the vehicle and an engine torque transmitted to a drive shaft by driving an assist motor.
In case the brake is applied and the clutch is released, the speed of the ring gear of the transmission increases in comparison with the engine speed. On the contrary, in case the brake is released and the clutch is applied, the output shaft of the engine and the ring gear of the transmission rotate integrally. Besides, the hybrid vehicle having a plurality of prime movers such as the engine and the motor generator is disclosed also in Japanese Patent Laid-Open No. 2002-78105, Japanese Patent Laid-Open No. 2000-142146, and Japanese Patent Laid-Open No. 2003-32802.
According to the hybrid vehicle taught by Japanese Patent Laid-Open No. 2000-346187, it is necessary to increase the speed of the motor functioning as the reaction element in order to increase the speed ratio between the speed of the carrier of the planetary gear unit and the speed of the drive shaft. That is, in order to run the vehicle at low speed by keeping the engine speed at a predetermined speed, the motor functioning as the reaction element has to have a high output so that the size of the motor may be large. In order to reduce the speed ratio between the speed of the carrier of the planetary gear unit and the speed of the drive shaft, a drive torque is applied to the sun gear of the planetary gear unit in a counter direction by reversing the motor, and a synthesis of the engine torque and the drive torque of the motor is outputted from the ring gear to the drive shaft. On the other hand, the assist motor carries out a regeneration of the energy and the generated electric power is supplied to the motor. Therefore, power circulation may occur.